216 LIVINGSTONE'S LAST JOURNALS. [Chap. VIIL 



area which this basalt covers extends from near the Vaal 

 Eiver in the south, to a point some sixty miles beyond the 

 Victoria Falls, and the average breadth is about 150 miles. 

 The space is at least 100,000 square miles. Sandstone rocks 

 stand up in it at various points like islands, but all are 

 metamorphosed, and branches have flowed off from the 

 igneous sea into valleys and defiles, and one can easily trace 

 the hardening process of the fire as less and less, till at the 

 outer end of the stream the rocks are merely hardened. 

 These branches equal in size all the rocks and hills that 

 stand like islands, so that we are justified in assuming the 

 area as at least 100,000 square miles of this basaltic sea. 



The molten mass seems to have flowed over in successive 

 waves, and the top of each wave was covered with a dark 

 vitreous scum carrying scoriae with angular fragments. This 

 scum marks each successive overflow, as a stratum from twelve 

 to eighteen inches or more in thickness. In one part sixty- 

 two strata are revealed, but at the Victoria Falls (which are 

 simply a rent) the basaltic rock is stratified as far as our 

 eyes could see down the depth of 310 feet. This exten- 

 sive sea of lava was probably sub-aerial, because bubbles 

 often appear as coming out of the rock into the vitreous 

 scum on the surface of each wave : in some cases they have 

 broken and left circular rings with raised edges, peculiar to 

 any boiling viscous fluid. In many cases they have cooled 

 as round pustules, as if a bullet were enclosed ; on breaking 

 them the internal surface is covered with a crop of beautiful 

 crystals of silver with their heads all directed to the centre 

 of the bubble, which otherwise is empty. 



These bubbles in stone may be observed in the bed of the 

 Kuruman River, eight or ten miles north of the village ; 

 and the mountain called " Amhan," west-north-west of the 

 village, has all the appearance of having been an orifice 

 through which the basalt boiled up as water or mud does in 

 a sreyser. 



